Abstract:

The main objectives of this study were to develop and analyze a seismic retrofit method for flared columns that are fixed at both ends and consist of a structural flare. The columns of Bridge I-1556 located in Sparks, Nevada, were used in the study. A previous study of the columns with respect to the seismic requirements had shown that the confinement steel is inadequate and the shear capacity near the base of the columns is marginal. Both of these deficiencies were addressed by using a glass fiber-epoxy jacket. Because the columns are flared, a continuous wrap over the flared segments is not appropriate. Therefore, for the flared segments, a series of overlapping straps were recommended . The FHWA and ACI procedures were used in design of the composite jacket. To determine the effectiveness of the retrofit, the as-built and retrofitted columns were analyzed for earthquakes loading using a nonlinear response history analysis computer program called RC-Shake. This program accounts for stiffness and strength degradation of reinforced concrete elements under cyclic loads. The 1994 Sylmar-Northridge earthquake record was used. It was found that the retrofit reduced the displacement ductility demand by 50 percent under an earthquake with PGA of 1.2g.